It has become a common practice to provide for some models of oscilloscopes an additional amplifier channel to provide the display of an external triggering signal as an additional viewing mode known as Trigger View. Generally, a sample of the external triggering signal is picked off at the trigger preamplifier or trigger comparator stage, amplified to a suitable level, and made available as a trigger view signal via a vertical display mode switch to the vertical deflection amplifier. Because the vertical and horizontal circuits of an oscilloscope are physically separated from each other, the trigger view signal path is necessarily a longer physical length than a normal vertical amplifier channel. This doesn't present a problem when the trigger view signal is the only signal displayed; however, a problem does become apparent when the trigger view signal is alternated with a signal processed by the normal vertical channel because the longer signal path length of the trigger view signal results in an approximate four nanosecond delay of the trigger view signal with respect to the normal vertical signal. In high-speed applications, for example, where the sweep timing is two nanoseconds per division, this effective delay is two full graticule divisions, rendering any timing comparisons impractical.
Heretofore suggested solutions to the problem addressed hereinabove have either been inadequate or have produced other problems. For example, designing the trigger view amplifier channel with a physical and electrical layout the same as the normal vertical channel is unnecessarily expensive, requiring unneeded parts and consuming circuit board space. It has been suggested to lengthen the normal vertical amplifier delay to match the trigger view channel delay; however, this proposed solution results in increased bulk, particularly where the normal vertical amplifier comprises matched channel 1 and channel 2 dual amplifiers, and further, lengthening the normal vertical amplifier channel delay may lead to electrical problems associated therewith. Another alternative, delaying the start of the sweep associated with the trigger view display, results in jitter and other timing and triggering problems.
The concept of trigger view is intended primarily as an ancillary oscilloscope feature for user convenience, and therefore economies of the situation dictate that problems associated therewith should not dominate instrument design to the detriment of other signal processing circuits or oscilloscope operating functions.